This invention relates generally to connectors for connecting tubular members in end-to-end relation. More particularly, it relates to an improved connector especially well suited for use in connecting tie-back risers to subsea wellhead systems.
Prior connectors of this type have required only minimal capacity because the risers were tied back to fixed structures at the water surfaces. However, with the advent of float production type vessels (i.e. TLP, or SPAR), the required capacity of the connectors was increased due to the motion of the drilling vessel. Therefore, the connectors used in these applications were typically modified drilling connectors with large outside diameters.
On a SPAR type vessel, the risers are supported at the top with a buoyant air can system. The ID of these air cans must be sized to pass the tie-back connector OD, and the use of these large OD connectors resulted in large air can inner stems that increased the air can weight while reducing the buoyancy. As a result, the need for a slim OD external tie-back connector arises as water depths get deeper, and resulting riser weights get higher.
Thus, it is the primary object of this invention to provide a slim OD connector for this and other purposes.
Another object is to provide such a connector which is highly efficient in that it requires minimal operating pressure.
These and other objects are accomplished by a connector of this type which comprises, in its illustrated and preferred embodiment, first and second tubular members adapted to be disposed in end-to-end relation, each member having locking grooves thereabout adjacent its end, a first sleeve having one end carried about the first member for axial reciprocation with respect thereto and having its opposite end surrounding the end of the second member, when the members are arranged in end-to-end relation, and a second sleeve having one end carried about the first member and within the first sleeve for axial reciprocation with respect thereto. A radially expandable and contractible ring having axially spaced first and second teeth about its inner side is carried within the sleeves to permit it to be moved with the first sleeve over the end of the first member, when the sleeves are in a first axial position relative to one another, to permit the ring to assume its normally expanded position, and thereby dispose the first and second teeth opposite the first and second grooves, respectively.
The sleeves have inner cam surfaces adjacent their ends which are slidable over cam surfaces about the outer sides of the ring to urge the ring and its teeth inwardly to locking position with the grooves about the tubular members, when the sleeves are moved axially toward one another, and to permit the ring to expand to unlocking position, when the sleeves are moved axially away from one another. More particularly, operating means connects the opposite ends of the sleeves for selectively moving them in one direction relative to one another, in order to move the ring to locking position, and in the opposite direction relative to one another to permit the ring to move to unlocking position. Thus, the connector provides high capacity while minimizing the required operating forces.
As illustrated, and in keeping with the need for a slim OD, the operating means preferably includes radially outwardly extending walls on the one end of the second sleeve sealable slidable within the one end of the first sleeve to form an annular space between them. A radially inwardly extending piston on the one end of the first sleeve intermediate the end walls is sealably slidable about the second sleeve to divide the space into fluid pressure chambers on its opposite sides, and means are provided by which operation fluid may be supplied to and from the chambers in order to selectively expand and contract the chambers and thereby move the ring between locking and unlocking positions.
Preferably, the inner and outer sides of the first and second sleeves have overlapping cam surfaces slidable over one another as the ring moves to locking position. It is also preferred that the connector includes means for preventing accidental displacement from its locked position by ratchet teeth and grooves on adjacent sides of the sleeves.
In accordance with another of its novel features, the connector may be provided with means external to the fluid pressure chambers for moving the sleeves to releasing position. As shown, this comprises a first abutment on the first sleeve, and a second abutment on the second sleeve which is axially spaced from the first abutment, whereby an extendible and retractable actuator may be installed between the abutments in order to move them axially apart.